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| United States Patent |
5,108,331
|
|
Shimada
, et al.
|
April 28, 1992
|
Method for manufacturing small tubular lamps
Abstract
In a method for manufacturing small tubular lamps, a moving amount of a
tube stock is adjusted according to a wall thickness thereof to make the
stock-guide amount uniform, and the internal pressure during the
stock-guide step is also adjusted so as to produce a suitable dimension of
the outside diameter thereof, whereby the working amount in the succeeding
step is reduced to decrease errors in dimensional tolerances, particularly
in wall thickness and internal volume.
| Inventors:
|
Shimada; Hiroharu (Yokohama, JP);
Yaguchi; Yasuhisa (Yamato, JP);
Muto; Masaaki (Kawasaki, JP)
|
| Assignee:
|
Stanley Electric Co., Ltd. (Tokyo, JP)
|
| Appl. No.:
|
744364 |
| Filed:
|
August 13, 1991 |
Foreign Application Priority Data
| Aug 17, 1990[JP] | 2-216521 |
| Jul 12, 1991[JP] | 3-197314 |
| Current U.S. Class: |
445/3; 65/109; 65/160; 445/22; 445/26 |
| Intern'l Class: |
H01J 009/00 |
| Field of Search: |
445/26,22,3
65/108,109,110,160,163,164,162
|
References Cited
U.S. Patent Documents
| 3263852 | Aug., 1966 | Fridrich | 445/26.
|
| 3305289 | Feb., 1967 | Fridrich | 445/26.
|
| 3576611 | Apr., 1971 | Obersby | 65/109.
|
| 3679385 | Jul., 1972 | Senft | 65/109.
|
| 3685880 | Aug., 1972 | Sobieski | 445/26.
|
| 4389201 | Jun., 1983 | Hansler et al. | 445/26.
|
| 4675043 | Jun., 1987 | Conta et al. | 65/160.
|
Primary Examiner: Ramsey; Kenneth J.
Attorney, Agent or Firm: Frishauf, Holtz, Goodman & Woodward
Claims
What is claimed is:
1. A method for manufacturing small tubular lamps, comprising:
forming a stock-guide by heating and melting a predetermined portion of a
glass tube stock while rotating the tube stock about an axis of the tube
stock and moving an end portion of the tube stock toward the center of the
tube stock to form a stock-guide portion; and
molding by re-heating and melting said stock-guide portion and forming it
into a predetermined shape by a mold;
said step of forming a stock-guide comprising:
adjusting a moving amount of the tube-stock end toward the center of the
tube stock as a function of a sectional area of said tube stock so that a
glass volume of the stock guide portion is substantially constant; and
applying an internal pressure higher than atmospheric pressure in a range
of 2 to 6 mmHg into said tube stock to maintain an outside diameter of a
center portion of said stock-guide portion substantially constant; and
said molding step comprises:
forming a female shape, corresponding to a completed state of the lamp, in
the end of a roller;
placing said roller, movable in a diametrical direction of said tube stock,
in pressure contact with said reheated and molten stock-guide portion; and
rotating said tube stock until said roller reaches a predetermined position
in contact with said reheated and molten stock-guide portion to shape said
stock-guide portion.
2. The method of claim 1, wherein said tube stock comprises a glass tube.
3. The method of claim 1, wherein aid tube stock comprises a quartz tube.
4. The method of claim 1, wherein said molding is carried out by a roller
having said female shape on a circumferential surface thereof.
5. The method of claim 1, wherein said tube stock is heated and re-heated
by a burner.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method for manufacturing small tubular
lamps used for discharge lamps such as small metal halide lamps.
2. Description of the Prior Art
In manufacturing a small tubular lamp, for example, as shown in FIGS. 4 and
5, a tube stock a formed of glass, quartz, etc. is set on a glass lathe or
a working device provided with a function similar to that of the glass
lathe. At least one of left and right collets (bearings) is moved by a
predetermined amount toward the center, while heating the tube stock a by
a burner b in a rotating state, whereby padding is gathered on a
predetermined portion of the tube stock a.
Then, the tube stock a is fully heated and made molten, and thereafter the
predetermined portion of the tube stock a is covered with a mold c for
blow molding. A predetermined pressure is applied into the tube stock a to
inflate and suitably shape the tube stock a.
In metal vapor discharge lamps such as metal halide lamps, vapor pressure
of a luminous material sealed into a luminous tube greatly influences the
output, light color, etc. Therefore, it is desirable to minimize
unevenness between individuals luminous tubes. Because of this, it is
demanded in the process of manufacturing a luminous tube that dimensions
of various parts, volumes, etc. need to have reproducibility with high
precision.
Particularly, in a metal halide lamp whose power consumption is low
(specifically, 100 W or less), severe improvement in precision is demanded
with the trend of smaller types. The aforementioned conventional
manufacturing method is not absolutely fulfilled with the aforesaid
demand. Despite the fact that for example, a demand for a headlamp for an
automobile or the like of which power consumption is low is anticipated,
yield is poor and cost is high, thus posing a problem in that they cannot
be sufficiently supplied to the market.
It is an object of the present invention to provide a method for
manufacturing small tubular lamps capable of molding small tubular lamps
with high working precision and with low cost.
SUMMARY OF THE INVENTION
For solving the aforementioned problems, the present invention provides a
method for manufacturing small tubular lamps comprising the steps of
forming a stock-guide by heating and melting a predetermined portion of a
tube stock while rotating the tube stock about an axis of the tube and
moving a tube end toward the center to form a stock-guide portion, and
molding by re-heating and melting said stock guide and forming it into a
predetermined shape by a mold, characterized in that said stock-guide
forming step adjusts a moving amount of the tube end toward the center
according to a sectional area of said tube stock so that a glass volume of
the stock guide portion is constant and applies internal pressure higher
than suitable atmospheric pressure in a range of 2 to 6 mmHg into said
tube stock to maintain an outside diameter of the center of said stock
guide portion substantially constant, and said molding step is carried out
by forming a female shape in a completed state in the end of a disk,
placing a roller movable in a diametrical direction of said tube stock in
pressure contact with said reheated and molten stock guide portion and
rotating said tube stock until said roller reaches a predetermined
position. With the above-described manufacturing method, precision in the
manufacture process is improved to solve the aforesaid problem.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows an inert gas piping system and control circuit showing one
embodiment of a method for manufacturing a small tubular lamp according to
the present invention;
FIG. 2 is a front view in an enlarged scale showing principal parts of the
embodiment shown in FIG. 1;
FIG. 3 is a side view in an enlarged scale showing principal parts shown in
FIG. 1;
FIG. 4 illustrates a conventional step of forming a stock-guide; and
FIG. 5 illustrates a conventional molding step.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The present invention will be described hereinafter by way of an embodiment
shown in the drawings.
In FIG. 1, reference numeral 1 designates a tube stock. Opposite ends of
the tube stock (a glass tube, a quartz tube, etc.) I are airtightly held
by collets 2A and 2B. The collets 2A and 2B can be moved by a suitable
distance in an axial direction of the glass tube 1 by pulse motors 3A and
3B. A burner 4 is arranged in the middle between the collets 2A and 2B.
In FIG. 1, the solid line indicates piping of inert gas, and the dash line
indicates an electrical wiring. The inert gas flows through a needle valve
5 and a flow meter 6 and is branched into a direction of the glass tube 1
and a direction of a bypass 7. A valve 8A and a coupler 9A are interposed
between a branch point (inlet of the bypass 7) and one end of the glass
tube 1. The inert gas is once branched to bypass 7 and passes through
respective flowpassages, after which the gases are again joined together.
The joined gases are discharged passing through a variable valve 10 with
an actuator. A fine differential pressure gauge 11 is provided at the
aforesaid branch point.
The fine differential pressure gauge 11 measures a pressure difference
between the atmospheric pressure and inert gas line, and the measured
signal is supplied to a PID control unit 12. The PID control unit 12
drives the variable valve 10 according to a difference between a preset
pressure and an actual pressure and is operated so as to maintain the
pressure of the inert gas line constant.
The pulse motors 3A and 3B are driven by drivers 13A and 13B which receive
an output pulse of a pulse oscillator 14. The pulse oscillator 14 is
controlled by a microcomputer 15.
In FIG. 1, reference numeral 20 designates a roller. The roller 20 is
provided for the molding step applied to the tube stock 1, the structure
of the roller 20 being shown in detail in FIG. 2 and FIG. 3. Above the
tube stock 1 is rotatably supported, by an arm 2., a disk-like roller 20
formed of carbon or the like and formed at an end with a female shape (see
FIG. 2 in a completed state of a tubular lamp as an object. The arm 21 is
rotated about a fulcrum provided in a column 26 according to a position of
a cam 22 driven by a bowl screw 23 to displace the roller 20 along the
diametric direction of the tube stock 1. A position detection bar 25 is
provided on the arm 21, and a position sensor 24 is actuated when the
position detection bar 25 reaches a predetermined position to notify that
state.
The method for manufacturing a small tubular lamp according to the present
invention will be described hereinafter in accordance with the following
sequential steps.
(1) Premeasured inside diameter and outside diameter of the glass tube 1
are inputted into a microcomputer (micon) 15.
(2) The micon 15 computes adequate stock-guide amount and pressure in the
glass tube 1 from a sectional area of the glass tube 1.
(3) Upon receipt of command from the micon 15, the PID control unit 12
manipulates the variable valve 10 to stabilize the inert gas line at
computed pressure in the range of 2 to 6 mmHg.
(4) After the glass tube 1 has been molten by the burner 4, the pulse
oscillator 14 is actuated in accordance with the command of the micon 15,
and the computed number of pulse signals are sent to the drivers 13A and
13B to drive the pulse motors 3A and 3B. Thereby, the collets 2A and 2B
are moved by the computed distance in the direction of the center, whereby
the stock-guide step is executed and next, the molding step proceeds
(5) A predetermined portion of the tube stock 1 is again heated and made
molten, and the cam 22 is driven to move down the roller 20, which is
placed in pressure contact with the tube stock 1 by its own weight.
(6) A position of the roller 20 is detected by the position detection bar
25, and the step (5) above is repeated until the roller 20 reaches a
predetermined position.
(7) Upon termination of the aforesaid steps, a portion in contact with the
roller 20 is re-heated to remove distortion.
The function and effects of the method for manufacturing small tubular
lamps using the above-described steps according to the present invention
will be described hereinafter.
(1) First, the stock-guide amount is adjusted by the stock-guide step
according to a sectional area of the tube stock 1, whereby a volume of
glass material of a portion formed as a luminous tube can be maintained
constant by the succeeding step.
(2) At that time, an internal pressure of the tube stock 1 is set to an
adequate pressure within the range of 2 to 6 mmHg, whereby the outside
diameter of the center portion of the stock-guide portion can be
maintained substantially constant and substantially equal to the outside
diameter of the tubular lamp to be completed by the succeeding step.
(3) Furthermore, the outside diameter of the center portion is made
substantially constant and equal in the outside diameter to that of the
completed state as described above, whereby the molding step by the roller
20 is to have its object principally for arranging the shape. The working
amount decreases, and therefore the lowering of the accuracy in the
molding step can be reduced. By the functions described in the above
paragraphs (1) to (3), excellent dimensional accuracy and tubular lamps
excellent in standardization of shapes are obtained.
Table 1 shows specific measured values of a center outside diameter, a
center inside diameter and an internal volume of tubular lamps which are
extremely small. Such tubular lamps for discharge are called a double end
type have a center outside diameter of 6 mm and a length of tube of 7.5 mm
except a seal portion manufactured by the method according to the present
invention. A dimension tolerance in the center outside diameter is 0.03
mm, and particularly, a dimension tolerance even in the center inside
diameter is 0.07 mm which has been heretofore considered to be difficult
to obtain. Uniformity with such high precision can be realized with the
present invention. As a result, an internal volume which is an integrated
value of the respective dimensional accuracy is also 1.8.times.10.sup.-3
cc. Thus, the dimensions of various portions are uniformly formed with
extremely high accuracy. It is therefore readily assumed that a discharge
lamp, for example, such as a metal halide lamp which employs a tubular
lamp produced by use of the present invention, also has a high uniformity.
TABLE 1
______________________________________
Internal
Center outside
Center inside
volume
Materials No.
diameter (mm)
diameter (mm)
(.times. 10.sup.-3 cc)
______________________________________
1 6.01 2.99 29.7
2 6.03 3.02 30.5
3 6.00 2.99 29.4
4 6.03 3.06 31.2
5 6.02 3.02 30.2
______________________________________
As described above, according to the present invention, the stock-guide
amount is adjusted according to a sectional area of a tube stock, and in
addition, suitable internal pressure is applied during the stock-guide
step so that the outside diameter may have a predetermined dimension,
whereby the working amount in the succeeding working step can be extremely
reduced to render possible molding a tubular lamp with high accuracy, and
unevenness of the lamp characteristics can be reduced. Accordingly, small
metal halide lamps can be used even for uses which have been heretofore
difficult to be applied. Moreover, the stock-guide position, stock-guide
amount, pressure difference between inside and outside of a tube stock,
etc. can be controlled by a microcomputer to thereby freely mold any
dimension and shape. Furthermore, the dimensional allowance of the tube
stock is improved, and selection of materials becomes unnecessary. Tubular
lamps can be produced with low cost.
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